Biomedical subjects

James M Wild

Publications and source records attributed to James M Wild.

4 recordsLinked to original sources

PubMed2006

Simultaneous parallel inclined readout image technique.

Sensitivity-encoded phase undersampling has been combined with simultaneous slice excitation to produce a parallel MRI method with a high volumetric acquisition acceleration factor without the need for auxiliary stepped field coils. Dual-slice excitation was produced by modulating both spin and gradient echo sequences at +/-6 kHz. Frequency aliasing of simultaneously excited slices was prevented by using an additional gradient applied along the slice axis during data acquisition. Data were acquired using a four-channel receiver array and x4 sensitivity encoding on a 1.5 T MR system. The simultaneous parallel inclined readout image technique has been successfully demonstrated in both phantoms and volunteers. A multiplicative image acquisition acceleration factor of up to x8 was achieved. Image SNR and resolution was dependent on the ratio of the readout gradient to the additional slice gradient. A ratio of approximately 2:1 produced acceptable image quality. Use of RF pulses with additional excitation bands should enable the technique to be extended to volumetric acquisition acceleration factors in the range of x16-24 without the SNR limitations of pure partially parallel phase reduction methods.

Algorithms↗

PubMed2004

Strategy for the spectral filtering of myo-inositol and other strongly coupled spins.

A multiple quantum filter strategy is presented for spectrally discriminating metabolites with strongly coupled spins from those whose spins are either uncoupled or weakly coupled. The strategy also includes a means for selectively suppressing the background multiplets of metabolites that also have strongly coupled spins. As a demonstration of its efficacy at 3.0 T, the strategy is shown to enhance by a factor of approximately 5 the signal-to-background ratio of the myo-inositol band at 3.6 ppm relative to that in response to a PRESS sequence with the same sequence timings. This is done by eliminating the uncoupled resonance of glycine and the weakly coupled multiplets of glutamate and glutamine, and by selectively suppressing the strongly coupled taurine multiplet 3-fold. The macromolecular background was effectively removed through its transverse decay over 105 ms. The associated cost of gaining the signal to background enhancement is a drop in signal yield by a factor of 0.75 relative to PRESS at the same timings. The myo-inositol signal to noise ratio was nevertheless maintained by the filter at approximately 12.

Adult↗

PubMed2003

B1AC-MAMBA: B1 array combined with multiple-acquisition micro B0 array parallel magnetic resonance imaging.

The combination of an in-plane B(1) sensitivity encoding (SENSE) technique with a simultaneous multiple-slice B(0) field step technique (multiple-acquisition micro B(0) array (MAMBA)) has produced high scan time reduction factors (R < or = 8). In this study, two slices were acquired simultaneously in combination with x2 and x4 SENSE in-plane encoding using a MAMBA stepped B(0) field coil inside a four-channel phased-array coil system. Experiments were performed on a 1.5 T Infinion system (Philips Medical Systems, Cleveland, OH). The signal-to-noise ratio (SNR) was reduced with higher R factors, as was expected from the reduced number of acquisitions used to create the unaliased images. The combination of SENSE and MAMBA offers great promise for reducing scan times through parallel acquisition while at the same time reducing the number of RF channels required by a factor equal to the number of field steps employed. The B(1) array combined with MAMBA (B(1)AC-MAMBA) technique is applicable when the length of an object is much greater than its diameter, as in scanning limbs or in whole-body screening for disease.

Artifacts↗

PubMed2002

Interleaved pulsed MAMBA: a new parallel slice imaging method.

A method of acquiring slices in parallel is described which uses interleaved sets of pulsed B(0) field coils to generate discrete regions of uniform field within the main magnetic field known as interleaved MAMBA (multiple acquisition micro B(0) array). Simulations of a number of coil designs were performed using the Biot-Savart law. A six-step coil was built and interfaced to a 0.17 T Niche MRI system and the field steps measured using an imaging technique. Measured field steps were in good agreement with the values predicted by simulation. The coil design was then scaled up by a factor of three, interfaced to a 1.5 T whole-body MRI system, and scans of the hands and arms of volunteers were acquired from up to four field steps using standard spin and gradient echo sequences. Images were also acquired simultaneously from two field steps with no frequency encode aliasing and one excitation. The one-dimensional interleaved pulsed MAMBA step field technique shows great promise for enabling many slices to be acquired simultaneously along the axis of the coil for rapid volumetric studies without the need for multiple shot Hadamard encoding. Extension of interleaved coil design to two or three dimensions is feasible, which could provide full spatial coverage combined with ultra-rapid data acquisition.

Echo-Planar Imaging↗